JP2000259130A - Liquid crystal display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain at low cost the liquid crystal display device which can improve the color reproducibility of a field sequential color system by preventing even video including movements from blurring or trailing by increasing the response speed of a liquid crystal. SOLUTION: The liquid crystal display device has liquid crystal capacity constituted between a pixel electrode and a common electrode connected to a switching element and auxiliary capacity constituted between the pixel electrode and an auxiliary electrode (or gate electrode). A video signal application period wherein a voltage corresponding to a video signal is applied between the pixel electrode and common electrode and an auxiliary signal application period wherein a voltage corresponding to an auxiliary signal is applied are included and at least one of the common voltage Vc and auxiliary voltage Va is made different between the video signal application period and auxiliary signal application period. The response speed of the liquid crystal can be made fast by applying different voltages V1c corresponding to the video signal to the liquid crystal capacity in the video signal application period and auxiliary signal application period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television set, a computer, a word processor and an OA (Operating System).
The present invention relates to a liquid crystal display device used for a device automation device and the like and a driving method thereof.

[0002]

2. Description of the Related Art FIG. 13 shows an equivalent circuit in a general active matrix driving type liquid crystal display device.

This liquid crystal display device has a plurality of gate electrodes 4.
One and a plurality of source electrodes 42 are provided to intersect with each other, and a switching element 43 such as a thin film transistor is provided near the intersection of the two electrodes. Gate electrode 41
A pixel electrode 44 is provided for each of the matrix-shaped regions separated by the source electrode 42, and is connected to the source electrode 42 via the switching element 43. The pixel electrode 44 is disposed with a liquid crystal layer (not shown) interposed between the pixel electrode 44 and a common electrode 45, and a liquid crystal capacitor 46 is formed between the two electrodes. An image is displayed by writing and holding an arbitrary voltage in the liquid crystal capacitor 46.

FIG. 1 shows a general driving voltage waveform of such an active matrix driving type liquid crystal display device.
It is shown in FIG.

The gate voltage V applied to the gate electrode 41
As g, a pulse waveform of an ON voltage Vgh for turning on the switching element is applied line-sequentially in one field period, and one screen is scanned. As the source voltage Vs applied to the source electrode 42, a video signal corresponding to a row in which the ON voltage Vgh is input to the gate electrode 41 is sequentially applied. ± Vcac is applied to the common electrode 45 as the common voltage Vc, and a new source voltage Vs is written to the pixel electrode 44 as the pixel voltage Vp every time the on-voltage Vgh is applied to the gate electrode 41. as a result,
The difference between the pixel voltage Vp and the common voltage Vc is the liquid crystal applied voltage V
1c is applied to the liquid crystal layer.

The liquid crystal applied voltage Vl applied to this liquid crystal layer
FIG. 15 shows the relationship between c and the transmittance as an example of a TN (twisted nematic) type normally white mode used as a general liquid crystal mode.

Output range of source voltage Vs ± Vsmax
Is usually set to a voltage difference between a voltage Vlca at which a transmittance of 100% is obtained and a voltage Vlcc at which a transmittance of about 1% is obtained. The reason is that if the output range of the source voltage Vs is increased, a source driver having a high withstand voltage is required, which causes an increase in cost. Therefore, the output range of the source voltage Vs is set to the minimum range in which a sufficient contrast for practical use can be obtained. This is because Therefore, the source voltage Vs and the common voltage Vc are set as shown in the following equation with respect to the liquid crystal applied voltage Vlc.

[0008]

(Equation 1)

Next, the response of the transmittance of the liquid crystal panel is shown in FIG. In this figure, the solid line indicates the transmittance change when the video signal is changed from white display to black display to white display, and the transmittance change when the video signal is changed from white display to halftone display to white display. Is indicated by a broken line.

[0010] As shown in FIG.
When the display is changed from black display to white display, the response of the transmittance is almost completed within one field period. However, when the video signal is changed from white display to halftone display to white display, 1 is displayed.
The transmittance has not changed to the transmittance corresponding to the video signal within the field period. As described above, the response speed may be slow especially between video signals having a small applied voltage difference.

[0011] Such a liquid crystal display device has a sufficient performance with respect to image quality such as contrast, brightness and color reproducibility as compared with a display device such as a CRT. ing. However, when displaying a moving image, the response speed is slow as described above, so that the image may be observed as blurred or the outline may appear to be trailing. CRT
However, there is a problem in using it as a display device that can be used as a substitute for a display device.

Japanese Patent Application Laid-Open No. 56-27198 discloses a display device which obtains a color display by combining a black-and-white liquid crystal panel and a light source whose emission color switches to red, blue and green. This method is called a field sequential color method.

In the field sequential color system, the light emission color of the light source is switched to red, blue, and green, and at the same time, an image corresponding to each light emission color is sequentially displayed on the liquid crystal panel and driven. Even in the case of an image, the video signal changes each time it is written. Therefore, when the response of the liquid crystal panel is insufficient, continuous color information is mixed and color reproducibility is reduced, and it is difficult to obtain sufficient display performance.

As described above, the slow response speed of the liquid crystal panel causes a decrease in display performance, and the following methods have been proposed to improve this.

For example, Japanese Patent Laying-Open No. 4-42211 proposes a method of writing a voltage of an auxiliary signal different from a video signal before writing a voltage corresponding to the video signal. This method utilizes the fact that the effective response speed of the liquid crystal can be increased by applying a voltage higher or lower than this voltage to the liquid crystal layer before applying the voltage corresponding to the video signal. It is said that it is possible to improve the quality of moving images.

Alternatively, “SID 98 DIGEST
P. 143 A Novel Wide-Viewwin
g Angle Motion-Picture LC
D "proposes a method of writing and scanning the voltage of the auxiliary signal before writing and scanning the voltage corresponding to the video signal. According to this method, it is described that the quality of a moving image can be improved by erasing the video display already written.

Further, Japanese Patent Application Laid-Open No. Hei 9-138421 discloses that before writing and scanning a voltage corresponding to a video signal, all the scanning lines are simultaneously written to supply a variable common voltage of a common electrode. Has proposed a driving method for writing the voltage of the auxiliary signal.

If these improvement methods are applied to the above-described field sequential color system, it is possible to prevent a decrease in color reproducibility.

[0019]

As described above, in addition to the period for applying a voltage corresponding to a video signal to a liquid crystal panel, a period for applying a voltage of an auxiliary signal which is not an original video signal is provided. In addition, it is possible to increase the response speed of the liquid crystal. However, in order to effectively improve the response speed of the liquid crystal, it is important to appropriately set the voltage value of the auxiliary signal and the period for applying the auxiliary signal.

In general, the larger the amount of change in the voltage applied to the liquid crystal layer, the more energy can be applied to the liquid crystal molecules to increase the response speed. Therefore, it is preferable that the voltage value of the auxiliary signal be set to a voltage value exceeding the voltage range corresponding to the video signal. Further, it is preferable that the auxiliary signal can be set to a different voltage value according to the voltage corresponding to the video signal.

Furthermore, in the above-described driving method, the response time of the liquid crystal panel to which the applied auxiliary signal is applied is increased in order to increase the response speed of the liquid crystal panel by utilizing the transient response during the application of the auxiliary signal. It is preferable to be able to set the optimum value for the characteristics.

However, in the above-described driving method, it is difficult to effectively improve the response speed of the liquid crystal due to operational restrictions as described below.

In the method disclosed in JP-A-4-42211,
Before writing the voltage corresponding to the video signal from the source electrode to the pixel electrode via the switching element, the voltage of the auxiliary signal different from the video signal is written to the pixel electrode from the source electrode via the switching element. Therefore, in order to apply a voltage exceeding the voltage range corresponding to the video signal to the liquid crystal layer by the auxiliary signal, it is necessary to increase the withstand voltage of the source driver for inputting the signal voltage to the source electrode, and the manufacturing cost is reduced. Will increase. Further, since the auxiliary signal is written via the switching element, it is necessary to write the auxiliary signal in a short period other than the period for writing the voltage corresponding to the video signal. For this reason, it is indispensable to dramatically improve the ON performance of the switching element, and it is difficult to put it to practical use.

Alternatively, "SID 98 DIGEST
P. 143 A Novel Wide-Viewwin
g Angle Motion-Picture LC
In the method of "D", scanning for writing the voltage corresponding to the video signal from the source electrode to the pixel electrode via the switching element and scanning for writing the voltage of the auxiliary signal from the source electrode to the pixel electrode via the switching element are repeatedly performed. I have. Even in this method, in order to apply a voltage exceeding the voltage range corresponding to the video signal to the liquid crystal layer by the auxiliary signal,
It is necessary to increase the withstand voltage of the source driver for inputting the signal voltage to the source electrode, which increases the manufacturing cost. Furthermore, since the video signal cannot be displayed during the period when the auxiliary signal is applied to the liquid crystal panel, it is preferable to set this period short in order to prevent the brightness of the screen from being reduced. Is preferably set to the minimum period necessary for the response of the liquid crystal. However, in order to shorten the period in which the auxiliary signal is applied to the liquid crystal panel by this driving method, it is necessary to shorten the auxiliary signal writing scanning period. For this purpose, it is necessary to increase the size of the switching element in order to improve the ON performance of the switching element, and this causes a problem such as an increase in the defect occurrence rate of the switching element, which causes an increase in cost. .

Further, in the method disclosed in Japanese Patent Application Laid-Open No. Hei 9-138421, a voltage of an auxiliary signal is applied to all the scanning lines at a time in a write state, so that a constant voltage is applied to all pixels as an auxiliary signal. . However, in an actual video display, since a voltage corresponding to a video signal is different for each pixel, in order to reduce a response time for each pixel to reach a transmittance corresponding to the video signal, a different video is used for each pixel. It is necessary to set an auxiliary signal corresponding to the signal. Therefore,
With a constant auxiliary signal regardless of the video signal, the response speed cannot be effectively improved. Further, at the time of writing the auxiliary signal, the gate electrodes are simultaneously in a write state, and the capacitance load per source electrode increases. Therefore, a high-performance source driver capable of driving the increased capacitance load is required. .

In addition, in any of the driving methods described above, since the voltage of the auxiliary signal is applied via the switching element, the power consumption of the source driver increases when the auxiliary signal is applied, resulting in low power consumption. The characteristics of the liquid crystal display device are impaired.

The present invention has been made in order to solve the problems of the prior art, and has been made to increase the response speed of the liquid crystal, prevent blurring and tailing even in a moving image, and provide a field sequential color system. It is an object of the present invention to provide a liquid crystal display device and a driving method thereof capable of improving the color reproducibility of a liquid crystal display device, reducing manufacturing costs and reducing power consumption.

[0028]

According to the liquid crystal display device of the present invention, a switching element and pixel electrodes connected to the switching element are provided in a matrix, and the switching elements and the pixel electrodes are arranged via a liquid crystal layer. What is claimed is: 1. A liquid crystal display device comprising: a common electrode; and an auxiliary electrode forming an auxiliary capacitance between the pixel electrode and the pixel electrode, wherein a voltage corresponding to a video signal is applied between the pixel electrode and the common electrode. A video signal application period, and an auxiliary signal application period in which a voltage corresponding to an auxiliary signal is applied between the pixel electrode and the common electrode,
At least one of the common voltage applied to the common electrode and the auxiliary voltage applied to the auxiliary electrode is different between the video signal application period and the auxiliary signal application period,
Thereby, the above object is achieved.

According to the liquid crystal display device of the present invention, a switching element and a pixel electrode connected to the switching element are provided in a matrix, and a common electrode is arranged on the pixel electrode via a liquid crystal layer. A liquid crystal display device in which an auxiliary capacitor is formed between the pixel electrode and the gate electrode of the switching element, wherein a voltage corresponding to a video signal is applied between the pixel electrode and the common electrode. And an auxiliary signal application period during which a voltage corresponding to an auxiliary signal is applied between the pixel electrode and the common electrode, wherein a common voltage applied to the common electrode and a gate electrode applied to the gate electrode Is different between the video signal application period and the auxiliary signal application period,
Thereby, the above object is achieved.

According to the method of driving a liquid crystal display device of the present invention, a switching element and a pixel electrode connected to the switching element are provided in a matrix, and a common electrode disposed via a liquid crystal layer with respect to the pixel electrode. A method of driving a liquid crystal display device having an auxiliary electrode forming an auxiliary capacitor between the pixel electrode and the pixel electrode, wherein a voltage corresponding to a video signal is applied between the pixel electrode and the common electrode. Video signal application period, and an auxiliary signal application period for applying a voltage corresponding to an auxiliary signal between the pixel electrode and the common electrode, and at least one of the common electrode and the auxiliary electrode, Different voltages are applied between the video signal application period and the auxiliary signal application period, thereby achieving the above object.

According to the driving method of a liquid crystal display device of the present invention, a switching element and pixel electrodes connected to the switching element are provided in a matrix, and a common electrode is arranged on the pixel electrode via a liquid crystal layer. A method for driving a liquid crystal display device in which an auxiliary capacitance is formed between the pixel electrode and a gate electrode of the switching element, wherein a voltage corresponding to a video signal is applied between the pixel electrode and the common electrode. A video signal application period to be applied, and an auxiliary signal application period for applying a voltage corresponding to an auxiliary signal between the pixel electrode and the common electrode, and at least one of the common electrode and the gate electrode, Different voltages are applied during the video signal application period and the auxiliary signal application period, thereby achieving the above object.

In the auxiliary signal application period, a voltage that changes to two or more states may be applied to at least one of the common electrode and the auxiliary electrode.

During the auxiliary signal application period, at least one of the common electrode and the gate electrode is
A voltage that changes to the above state may be applied.

The auxiliary signal application period is provided before and after a writing period in which a voltage corresponding to a video signal is written to the pixel electrode via the switching element, and a voltage between the pixel electrode and the common electrode is set to In the auxiliary signal application period before the writing period and the auxiliary signal application period after the writing period, the polarity may be shifted to the opposite polarity to the video signal application period.

The auxiliary signal application period may be set simultaneously for all pixels.

The auxiliary signal application period may be set according to the timing at which a voltage corresponding to a video signal is written to each pixel electrode.

[0037] Between the pixel electrode and the common electrode,
Preferably, a voltage exceeding a voltage range applied during the video signal application period is applied during the auxiliary signal application period.

One field period is constituted by at least two or more sub-field periods including the video signal application period and the auxiliary signal application period, and a voltage corresponding to a video signal of a predetermined color component is applied to each sub-field period. The voltage may be applied between the pixel electrode and the common electrode during the video signal application period.

The one field period may include a subfield period for displaying a red component, a subfield period for displaying a green component, and a subfield period for displaying a blue component.

Hereinafter, the operation of the present invention will be described.

In the present invention, the pixel electrode forming a liquid crystal capacitor between the pixel electrode and the common electrode forms a storage capacitor between the pixel electrode and the auxiliary electrode, or the pixel electrode forms a storage capacitor between the pixel electrode and the gate electrode of the switching element. Make up capacity. For this liquid crystal display device, a common electrode is applied during a video signal application period for applying a voltage corresponding to a video signal between the pixel electrode and the common electrode, and an auxiliary signal application period for applying a voltage corresponding to the auxiliary signal. And at least one of the auxiliary electrode, or at least one of the auxiliary electrode and the gate electrode,
Different voltages are applied. Therefore, different voltages according to the video signal can be applied to the liquid crystal layer between the video signal application period and the auxiliary signal application period without supplying the auxiliary signal voltage from the source driver as in the related art.

By applying a voltage that changes to two or more states to at least one of the common electrode and the auxiliary electrode or at least one of the common electrode and the gate electrode during the auxiliary signal application period, The response speed of the panel can be effectively increased. The number of changes can be appropriately set according to the response speed of the liquid crystal.

An auxiliary signal application period is provided before and after a writing period in which a voltage corresponding to a video signal is written to the pixel electrode via a switching element, so that a voltage between the pixel electrode and the common electrode is adjusted before the writing period. The response for eliminating the influence of the previously written video signal by shifting to the opposite polarity side with respect to the video signal application period between the auxiliary signal application period and the subsequent auxiliary signal application period, and By performing a transient response in the opposite direction, the response speed of the liquid crystal panel can be effectively increased with respect to any video signal.

If the above-mentioned auxiliary signal application period is set for all the pixels at the same time, the screen corresponding to the auxiliary signal and the screen corresponding to the video signal can be switched on the entire screen. Turning off the light source in the black display state improves the light use efficiency.

Alternatively, if the auxiliary signal application period is set according to the timing at which a voltage corresponding to a video signal is written to each pixel electrode, the write period and the auxiliary signal application period can be different for different rows in the pixel. Can be set at the same time.

By increasing the voltage range applied between the pixel electrode and the common electrode during the auxiliary signal application period and applying a voltage exceeding the voltage range applied during the video signal application period, the response speed of the liquid crystal is increased. Is effectively improved.

One field period is constituted by at least two or more sub-field periods including the video signal application period and the auxiliary signal application period, and a voltage corresponding to a video signal of a predetermined color component is applied to each sub-field period. By applying the voltage between the pixel electrode and the common electrode during the video signal application period, the response speed of the liquid crystal can be increased to prevent color information from being mixed, thereby enabling color display with good color reproducibility.

If the one field period includes a subfield period for displaying a red component, a subfield period for displaying a green component, and a subfield period for displaying a blue component, Full-color display with good color reproducibility is possible.

[0049]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is an equivalent circuit diagram in a liquid crystal display device of the present embodiment.

This liquid crystal display device has a plurality of gate electrodes 1.
And a plurality of source electrodes 2 are provided so as to intersect with each other, and a thin film transistor is provided as a switching element 3 near the intersection of the two electrodes. A pixel electrode 4 is provided in each of the matrix-shaped regions separated by the gate electrode 1 and the source electrode 2, and is connected to the source electrode 2 via the switching element 3. This pixel electrode 4 is a common electrode 5
And a liquid crystal layer (not shown) interposed therebetween.
A liquid crystal capacitor 6 is formed between the two electrodes. Further, an auxiliary capacitor 8 is formed between the pixel electrode 4 and the auxiliary electrode 7 in parallel with the liquid crystal capacitor 6.

FIG. 2 shows a driving voltage waveform of this liquid crystal display device.

One field period includes an auxiliary signal application period and a video signal application period. The auxiliary signal application period includes a writing period for writing a video signal to the pixel electrode 4 via the switching element 3.

The gate voltage Vg applied to the gate electrode 1 is an on-voltage V that turns on the switching element.
gh is scanned line-sequentially.

As the source voltage Vs applied to the source electrode 2, a voltage corresponding to the video signal of the row in which the ON voltage Vgh is input to the gate electrode 1 is sequentially applied during the writing period.

As the common voltage Vc to be applied to the common electrode 5, a rectangular wave having an amplitude of ± Vcac with inverted polarity is input.

As the auxiliary voltage Va applied to the auxiliary electrode 7, a voltage of ± Vcac is input in the first half of the auxiliary signal application period including the writing period, similarly to the common voltage Vc. A voltage shifted by ± ΔVa1st according to the polarity of the common voltage Vc during the period is input. Further, during the video signal application period, a voltage shifted by ± ΔVa2nd is input.

A new source voltage Vs is written to the pixel electrode 4 every time the ON voltage Vgh is applied to the gate electrode 1. The pixel voltage Vp is changed by the influence of the auxiliary capacitor 8 at the same time as the voltage of the auxiliary voltage Va changes. Also change. At this time, the variation ΔVp of the pixel voltage Vp substantially follows the following equation.

[0059]

(Equation 2)

Then, a difference between the pixel voltage Vp and the common voltage Vc is applied to the liquid crystal layer as a liquid crystal application voltage Vlc.

The liquid crystal applied voltage Vl applied to this liquid crystal layer
FIG. 3 shows the relationship between c and the transmittance. Note that, as the liquid crystal mode, a normally white mode which is a TN type and has a large transmittance when no voltage is applied is used.

Here, the output range of the source voltage Vs ± V
smax is the voltage Vlcg at which 100% transmittance is obtained.
And a voltage Vlci at which a transmittance of about 1% is obtained. The reason is that if the output range of the source voltage Vs is increased, a source driver having a high withstand voltage is required, which causes an increase in cost. Therefore, the output range of the source voltage Vs is set to the minimum range in which a sufficient contrast for practical use can be obtained. This is because

In this embodiment, the liquid crystal applied voltage Vlc
, The source voltage Vs, the common voltage Vc, and the auxiliary voltage Va are set as shown in the following equation.

[0064]

(Equation 3)

Therefore, even when the source voltage Vs is in the range corresponding to the video signal, a voltage in the range from Vlca to Vlcc corresponding to the video signal is applied as the liquid crystal applied voltage Vlc in the first half of the auxiliary signal application period. In the latter half of the auxiliary signal application period, a voltage in the range from Vlcd to Vlcf corresponding to the video signal is applied, and in the video signal application period, a voltage in the range from Vlcg to Vlci corresponding to the video signal is applied.

As described above, the liquid crystal application voltage Vlc obtained by adding the constant voltage difference ΔVp to the voltage corresponding to the video signal can be applied during the auxiliary signal application period, so that an effective voltage corresponding to each video signal can be obtained. An auxiliary signal can be set.

Next, the change in the transmittance of the liquid crystal layer in this embodiment will be described with reference to FIG. Here, a change in transmittance when a white display video signal and a halftone video signal are alternately displayed is shown.

As shown in this figure, in both the case where the display is changed from white display to halftone display and the case where the display is changed from halftone display to white display, completely black is displayed during the first half of the auxiliary signal application period. After reaching the display and showing a transient response in the white display direction during the latter half of the auxiliary signal application period, the transmittance of white display and halftone display changes according to the video signal during the video signal application period I have.

As described above, since the video signal can be written in the black display state, it is not affected by the previously written video signal. Further, since a transient response in the white display direction is added in the latter half of the auxiliary signal application period, even when the image changes to a halftone display in which the response of the liquid crystal is slow, the transmittance corresponding to the image signal during the image signal display period is also reduced. Can be varied up to

According to this embodiment, the amount of voltage change between the video signal application period and the auxiliary signal application period is constant irrespective of the video signal, and the response time of the liquid crystal can be effectively reduced for any video signal. Can be shortened. Therefore, a bright display can be obtained by shortening the auxiliary signal application period and lengthening the image signal application period in which image display is performed.

Furthermore, regardless of the video signal written to the pixel electrode in the previous field, black display can be performed during the auxiliary signal application period, so that it is not affected by the video signal written in the previous field. A bright display can be obtained by preventing blurring and tailing even in a moving image. Further, since the source driver only needs to output a voltage range corresponding to a video signal, it is not necessary to increase the withstand voltage of the auxiliary voltage, and it is possible to prevent an increase in cost.

In this embodiment, since the entire screen is simultaneously switched from the black display, which is the auxiliary signal display, to the video signal display, if the blinking operation is performed so as to turn off the light source during the period in which the entire screen is black display, Light use efficiency is improved and power consumption can be reduced.

Note that, when explaining ΔVp and the response speed of the liquid crystal panel, when ΔVp2nd is set to be large,
The change in the liquid crystal application voltage in the first half of the auxiliary signal application period increases to reach black display in a short period, but ΔVp2nd
Is too large, the response from the black display to the video signal display becomes slow. On the other hand, if ΔVp1st is set to a large value, the change in the liquid crystal application voltage in the latter half of the auxiliary signal application period increases. In particular, when the video signal is close to white display, the response in the white display direction is accelerated, and The response to the display is fast, but if ΔVp1st is too large, a response in the white display direction occurs even when the video signal is black, resulting in a slow response to the video signal display. Therefore, by optimizing ΔVp in consideration of the response performance of the liquid crystal, it is possible to effectively increase the response speed of the liquid crystal panel and shorten the auxiliary signal application period.

The setting of the writing period and the setting of the number of changes of the auxiliary voltage during the auxiliary signal application period are not limited to those described in the present embodiment, but can be set according to the response performance of the liquid crystal panel. Further, although the writing period is provided in the auxiliary signal application period, it may be provided in the video signal application period, and the auxiliary voltage Va may be provided in the auxiliary signal application period.
May be changed instead of changing the common voltage Vc.

The setting of the common voltage Vc, the auxiliary voltage Va, and the source voltage Vs is not limited to the present embodiment. For example, the setting may be such that the transmittance becomes 100% during the auxiliary signal application period. In this case, the light source may be turned on and off so as to turn off the light source during the video signal writing period.

The liquid crystal mode is not limited to the TN mode, and another mode may be used, and a normally black mode may be used.

(Embodiment 2) In this embodiment, an example in which the present invention is applied to a field sequential color type liquid crystal display device will be described.

FIG. 5 is an equivalent circuit diagram in the liquid crystal display device of the present embodiment.

This liquid crystal display device has a plurality of gate electrodes 2
One and a plurality of source electrodes 22 are provided to intersect with each other, and a thin film transistor is provided as a switching element 23 near the intersection of the two electrodes. Gate electrode 2
1 and a source electrode 22, a pixel electrode 24 is provided in each of the matrix-shaped regions, and a switching element 23 is provided.
Is connected to the source electrode 22 via the. The pixel electrode 24 is disposed with a liquid crystal layer (not shown) between the pixel electrode 24 and the common electrode 25, and a liquid crystal capacitor 26 is formed between the two electrodes. Further, the pixel electrode 24 and the auxiliary electrode 27o
An auxiliary capacitor 28 is formed in parallel with the liquid crystal capacitor 6 between dd and 27even. This liquid crystal display device has the same configuration as that of the first embodiment except that auxiliary electrodes 27odd and 27even are separately connected for each row and different signals are input.

FIG. 6 shows a driving voltage waveform of this liquid crystal display device.

One field period is composed of a subfield period corresponding to display of a red component, a subfield period corresponding to display of a green component, and a subfield period corresponding to display of a blue component. In addition, full color display is performed. Each subfield period includes an auxiliary signal application period and a video signal application, and the switching element 2 is connected to the pixel electrode 24 during the video signal application period.
3 includes a writing period for writing a video signal.

Gate voltage Vg applied to gate electrode 21
, The pulse waveform of the ON voltage Vgh for turning on the switching element is line-sequentially scanned.

Source voltage Vs applied to source electrode 22
During the writing period, a voltage corresponding to the video signal of the row to which the ON voltage Vgh is input is sequentially applied to the gate electrode 21. In the present embodiment, a voltage whose polarity is inverted is applied sequentially for each horizontal scanning period and each subfield period.

Common voltage Vc applied to common electrode 25
, A rectangular wave having an amplitude of ± Vcac with inverted polarity is input. In this embodiment, the polarity is inverted every horizontal scanning period and each subfield period.

The auxiliary voltages Vaodd and Vaeven applied to the auxiliary electrodes 27odd and 27even are ± V in the same manner as the common voltage Vc during the video signal application period.
The voltage of cac is input, and during the auxiliary signal application period, a voltage shifted by ± ΔVa according to the polarity of the common voltage Vc at the time of writing is input. Common voltage Vc at the time of writing
Are different for each row, the auxiliary voltages Vaodd, V
shift voltage ± ΔVa of auxiliary voltage Va at aeven
Have different polarities.

A new source voltage Vs is written to the pixel electrode 54 every time the on-voltage Vgh is applied to the gate electrode 51, but at the same time as the voltage of the auxiliary voltage Va changes, the pixel voltage Vp is influenced by the auxiliary capacitance 58. Also change.
At this time, the variation ΔVp of the pixel voltage Vp substantially follows the following equation.

[0087]

(Equation 4)

Then, a difference between the pixel voltage Vp and the common voltage Vc is applied to the liquid crystal layer as a liquid crystal application voltage Vlc.

The liquid crystal applied voltage Vl applied to this liquid crystal layer
FIG. 7 shows the relationship between c and the transmittance. The liquid crystal mode is OCB (Optically Compatible).
(ensured Bend) type and normally white mode.

Here, the output range of the source voltage Vs ± V
smax is a voltage Vlca at which 100% transmittance is obtained.
And a voltage difference Vlcc at which a transmittance of about 1% is obtained. The reason is that if the output range of the source voltage Vs is increased, a source driver having a high withstand voltage is required, which causes an increase in cost. Therefore, the output range of the source voltage Vs is set to the minimum range in which a sufficient contrast for practical use can be obtained. This is because

In this embodiment, the liquid crystal applied voltage Vlc
, The source voltage Vs, the common voltage Vc, and the auxiliary voltage Va are set as shown in the following equation.

[0092]

(Equation 5)

Therefore, even when the source voltage Vs is in the range corresponding to the video signal, a voltage in the range from Vlcd to Vlcf is applied during the auxiliary signal application period as the liquid crystal application voltage Vlc, and during the video signal application period. A voltage in a range from Vlca to Vlcc corresponding to a video signal is applied.

As described above, the liquid crystal application voltage Vlc obtained by adding a constant voltage difference ΔVp to the voltage corresponding to the video signal can be applied during the auxiliary signal application period, so that an effective voltage corresponding to each video signal can be obtained. An auxiliary signal can be set.

Next, the change in the transmittance of the liquid crystal layer in this embodiment will be described with reference to FIG. In this figure,
The change in transmittance when a video signal corresponding to bright green display is applied is indicated by a solid line, and the change in transmittance when a video signal corresponding to dark green display is applied is indicated by a dotted line.

When a bright green display is performed, the liquid crystal panel repeatedly displays the red component as a black display, a green component as a white display, and a blue component as a black display. Repeatedly displays the red component as black display, the green component as halftone display, and the blue component as black display.

As shown in this figure, in both the case of the bright green display and the case of the dark green display, the transmittance corresponding to the video signal of each color is obtained within each subfield period. Good color display is obtained.

In this embodiment, as shown in FIG. 7, the voltage during the auxiliary signal application period is set to a lower voltage side than the video signal application period. The reason is that in the liquid crystal mode used in the present embodiment, the liquid crystal response voltage is slower on the low voltage side than on the high voltage side, and by applying a low voltage during the auxiliary signal application period, priority is given to the liquid crystal mode. This is to speed up the response of the liquid crystal to the low voltage side.

Further, in the present embodiment, the liquid crystal application voltage during the auxiliary signal application period is not necessarily set to a voltage that has a constant transmittance for all video signals. Therefore, in the case of a video signal corresponding to black display, such as a subfield period of a red component and a blue component when performing green display, the liquid crystal applied voltage applied during the auxiliary signal application period corresponds to white display. Since it is higher than that of a video signal, the amount of change in the white display direction after the auxiliary signal application period is reduced to prevent unnecessary liquid crystal response, and to speed up the response to the transmittance corresponding to the video signal. be able to.

As described above, according to the present embodiment, the amount of voltage change between the video signal application period and the auxiliary signal application period is constant irrespective of the video signal, and the response time of the liquid crystal to any video signal is reduced. It can be shortened effectively. Since the response of the liquid crystal is fast, the application period of the auxiliary signal can be shortened and the application period of the video signal for displaying an image can be extended,
A bright display can be obtained.

Also, regardless of the video signal written to the pixel electrode in the previous field, the transmittance corresponding to the video signal can be obtained after the auxiliary signal application period. A display with good color reproducibility can be obtained without being affected.

Furthermore, the source driver only needs to be able to output a voltage range corresponding to the video signal, and it is not necessary to increase the breakdown voltage due to the auxiliary voltage, so that an increase in cost can be prevented.

Note that the video signal application period and the voltage shift amount Δ
Vp is not limited to that shown in the present embodiment, and may be set according to the response performance of the liquid crystal. Further, the writing period may be set to the auxiliary signal application period.

The setting of the common voltage Vc, the auxiliary voltage Va, and the source voltage Vs is not limited to the present embodiment. May be set to be applied during the auxiliary signal application period. Further, the liquid crystal mode is not limited to the OCB mode, and another mode may be used.

The structure of the liquid crystal display device is not limited to the present embodiment. For example, a voltage corresponding to a video signal written line-sequentially or dot-sequentially to a pixel capacitor connected to a plurality of scanning lines is applied after a writing scan. A liquid crystal display device of a type in which data is simultaneously transferred to pixel electrodes on the entire screen may be used.

(Embodiment 3) FIG. 9 is an equivalent circuit diagram in a liquid crystal display device of this embodiment.

This liquid crystal display device has a plurality of gate electrodes 3
One and a plurality of source electrodes 32 are provided to intersect with each other, and a thin film transistor is provided as a switching element 33 near the intersection of the two electrodes. Gate electrode 3
A pixel electrode 34 is provided for each of the matrix-shaped regions separated by the pixel electrode 1 and the source electrode 32.
Is connected to the source electrode 32 via the. The pixel electrode 34 is disposed with a liquid crystal layer (not shown) interposed between the pixel electrode 34 and the common electrode 35, and a liquid crystal capacitor 36 is formed between the two electrodes. Further, the pixel electrode 34 and the gate electrode 31
A storage capacitor 38 is formed in parallel with the liquid crystal capacitor 36. Although the gate electrode 31 is also used as an auxiliary electrode as described above, a dedicated auxiliary electrode may be formed.

FIG. 10 shows a drive voltage waveform of this liquid crystal display device.

One field period includes an auxiliary signal application period and a video signal application period. The auxiliary signal application period includes a writing period for writing a video signal to the pixel electrode 34 via the switching element 33. In the present embodiment, the timings of the auxiliary signal application period and the video signal application period are set for each row according to the write period.

Gate voltage Vg applied to gate electrode 31
For example, a write period in which a pulse waveform of the ON voltage Vgh for turning on the switching element is input, and an auxiliary signal application period in which the auxiliary signal voltage ± ΔV is applied in synchronization with the write period are line-sequentially scanned. Here, Vgn indicates the signal of the n-th gate electrode, and Vgn-1 indicates n-1.
5 shows a signal of a gate electrode at the third position.

The auxiliary signal voltage is changed before and after the writing period in the auxiliary signal application period. During the auxiliary signal application period after the writing period, a voltage obtained by adding the same ± Vcac voltage as the common voltage Vc to the off voltage Vgl is input. A voltage shifted by ± ΔVa1st is input. Further, in the auxiliary signal application period before the writing period, a voltage shifted by ± ΔVa2nd is input. Thus, in the present embodiment, the first embodiment
Further, instead of applying the auxiliary voltage to each row at the same time as in the second embodiment, scanning is performed for each row in accordance with the timing of the pulse waveform of the ON voltage Vgh.

Source voltage Vs applied to source electrode 32
During the writing period, a voltage corresponding to the video signal of the row where the ON voltage Vgh is input to the gate electrode 31 is sequentially applied. In the present embodiment, a voltage whose polarity is inverted is applied sequentially for each horizontal scanning period and each subfield period.

A common voltage Vc applied to the common electrode 35
, A rectangular wave having an amplitude of ± Vcac with inverted polarity is input. In this embodiment, the polarity is inverted every horizontal scanning period and each subfield period.

A new source voltage Vs is written to the pixel electrode 34 every time the on-voltage Vgh is applied to the gate electrode 31. However, when the auxiliary voltage ± ΔVa is applied to the gate electrode 31 as an auxiliary electrode, The pixel voltage Vp also changes due to the influence of the auxiliary capacitance 38. Here, Vpn is n
9 shows a pixel voltage of a pixel electrode forming an auxiliary capacitance between the pixel electrode and the third gate electrode. The change amount Δ of the pixel voltage Vp at this time
Vp generally follows the following equation.

[0115]

(Equation 6)

Then, a difference between the pixel voltage Vp and the common voltage Vc is applied to the liquid crystal layer as a liquid crystal application voltage Vlc.
Here, Vlcn indicates a voltage applied to the liquid crystal capacitance between the pixel electrode and the common electrode that constitute an auxiliary capacitance between the nth gate electrode.

The liquid crystal applied voltage Vl applied to this liquid crystal layer
FIG. 11 shows the relationship between c and the transmittance. As a liquid crystal mode, a normally black mode, which is a TN type and has a high transmittance when a voltage is applied, is used.

Here, the output range of the source voltage Vs ± V
smax is a voltage Vlca at which 100% transmittance is obtained.
And a voltage difference Vlcc at which a transmittance of about 1% is obtained. The reason is that if the output range of the source voltage Vs is increased, a source driver having a high withstand voltage is required, which causes an increase in cost. Therefore, the output range of the source voltage Vs is set to the minimum range in which a sufficient contrast for practical use can be obtained. This is because

In this embodiment, the liquid crystal applied voltage Vlc
, The source voltage Vs, the common voltage Vc, and the auxiliary voltage Va are set as shown in the following equation.

[0120]

(Equation 7)

Therefore, even when the source voltage Vs is in the range corresponding to the video signal, the liquid crystal applied voltage Vlc is set to the voltage corresponding to the video signal during the auxiliary signal application period before the writing period.
A voltage in the range from Icg to Vlci is applied, and during the auxiliary signal application period after the writing period, V corresponding to the video signal is applied.
A voltage in the range from lca to Vlcc is applied. Further, during the video signal application period, Vlc corresponding to the video signal is used.
A voltage in the range from d to Vlcf is applied.

As described above, the liquid crystal application voltage Vlc obtained by adding the constant voltage difference ΔVp to the voltage corresponding to the video signal can be applied during the auxiliary signal application period, so that an effective voltage corresponding to each video signal can be obtained. An auxiliary signal can be set.

Next, a change in the transmittance of the liquid crystal layer in the present embodiment will be described with reference to FIG. Here, a change in transmittance when a white display video signal and a halftone video signal are alternately displayed is shown.

As shown in this figure, in both the case where the display is changed from white display to halftone display and the case where the display is changed from halftone display to white display, the display is completely completed during the auxiliary signal application period before the writing period. After reaching black display and showing a transient response in the white display direction during the auxiliary signal application period after the writing period,
During the video signal application period, the transmittance changes to white display and halftone display according to the video signal.

As described above, since the video signal can be written in the black display state, it is not affected by the previously written video signal. Furthermore, since a transient response in the white display direction is added during the auxiliary signal application period after the writing period, the image change to the halftone display, in which the response of the liquid crystal is slow, corresponds to the transmission corresponding to the image signal in the image signal display period. The rate can be changed quickly.

In the case of a white display video signal, the liquid crystal applied voltage Vlc is equal to that of FIG. 1 in the auxiliary signal application period before the writing period.
1 in the auxiliary signal application period after the writing period, Vlcc in FIG. 11 during the video signal application period, and Vlcf corresponding to the video signal in the video signal application period. Vl in FIG.
ch, Vlcb in FIG. 11 during the auxiliary signal application period after the writing period, and Vlc corresponding to the video signal during the video signal application period.
ce. Thus, according to the present embodiment, as described above, the amount of voltage change between the video signal application period and the auxiliary signal application period is constant irrespective of the video signal, and the response time of the liquid crystal is reduced for all video signals. Can be shortened. Since the response of the liquid crystal is fast, the image signal application period during which image display is performed can be extended by shortening the auxiliary signal application period, and a bright display can be obtained.

Furthermore, regardless of the video signal written to the pixel electrode in the previous field, black display can be performed during the auxiliary signal application period, so that it is not affected by the video signal written in the previous field. A bright display can be obtained by preventing blurring and tailing even in a moving image. Further, since the source driver only needs to output a voltage range corresponding to a video signal, it is not necessary to increase the withstand voltage of the auxiliary voltage, and it is possible to prevent an increase in cost. Furthermore, in the present embodiment, the auxiliary signal application period can be arbitrarily set without changing the write period, so that a switching element having high charging capability is not required. The auxiliary capacitor according to the present invention also has an effect of compensating for a charge leakage in the case where the holding of the liquid crystal capacitor is insufficient.

[0128] The following describes ΔVp and the response speed of the liquid crystal panel. When ΔVp2nd is set to be large,
The change in the voltage applied to the liquid crystal during the auxiliary signal application period before the writing period increases to reach black display in a short period.
If Vp2nd is too large, the response from black display to video signal display will be slow. On the other hand, when ΔVp1st is set to be large, the change in the liquid crystal application voltage during the auxiliary signal application period after the writing period increases.
If st is too large, a response in the white display direction occurs even when the video signal is displayed black, and the response to the video signal display becomes slow. Therefore, by optimizing ΔVp in consideration of the response performance of the liquid crystal, it is possible to effectively increase the response speed of the liquid crystal panel and shorten the auxiliary signal application period.

The setting of the writing period and the setting of the number of changes in the auxiliary voltage during the auxiliary signal application period are not limited to those described in this embodiment, but can be set according to the response performance of the liquid crystal panel. Furthermore, although the auxiliary signal application period is provided before and after the writing period, the auxiliary signal application period may be provided only after the writing period.

The setting of the common voltage Vc, the auxiliary voltage Va, and the source voltage Vs is not limited to the present embodiment. For example, the normal white mode is used so that black display is obtained during the auxiliary signal application period. Is also good. Also, the liquid crystal mode is not limited to the TN mode, and another mode may be used.

When the driving method described in this embodiment is applied to the field sequential color system, it is only necessary to set so that all the rows are simultaneously in the video signal application period. As another method, a line to be irradiated with a light source may be scanned at the same time as a line during the auxiliary signal application period scans the screen.

In the above embodiment, both the common voltage and the auxiliary voltage during the video signal application period and the auxiliary signal application period,
Alternatively, both the gate voltage and the auxiliary voltage can be different. However, in this case, it is necessary that the amount of voltage change between the video signal application period and the auxiliary signal application period differs between the two voltages. Further, the shapes of the pixel electrode and the counter electrode can be comb-shaped.

[0133]

As described in detail above, according to the present invention, the response speed of the liquid crystal can be effectively increased with respect to any video signal, and the response speed of the liquid crystal is affected by the previously written video signal. Since there is no such phenomenon, blurring and tailing can be prevented even with moving images. Further, by applying the present invention to a field sequential color system, a color display excellent in color reproducibility can be obtained. further,
Since the period during which an image is displayed can be lengthened, a bright display can be obtained.

Even if the auxiliary signal voltage is not supplied from the source driver, different voltages corresponding to the video signal can be applied to the liquid crystal layer between the video signal application period and the auxiliary signal application period. There is no need to increase the cost, and the cost can be prevented from increasing. Further, since the auxiliary signal voltage is not supplied from the source driver, low power consumption can be achieved. Further, since a reduction in one horizontal scanning time can be prevented or reduced, a high-performance switching element is not required. Therefore, a liquid crystal display device having excellent display quality can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram for describing a liquid crystal display device according to a first embodiment.

FIG. 2 is a drive voltage waveform diagram for explaining a method of driving the liquid crystal display device according to the first embodiment.

FIG. 3 is a diagram illustrating a relationship between a liquid crystal applied voltage Vlc and a transmittance in the liquid crystal display device according to the first embodiment.

FIG. 4 is a diagram illustrating a change in transmittance of the liquid crystal display device according to the first embodiment.

FIG. 5 is an equivalent circuit diagram for describing a liquid crystal display device according to a second embodiment.

FIG. 6 is a drive voltage waveform diagram for describing a method of driving the liquid crystal display device according to the second embodiment.

FIG. 7 is a diagram illustrating a relationship between a liquid crystal applied voltage Vlc and transmittance in the liquid crystal display device of Embodiment 2.

FIG. 8 is a diagram illustrating a change in transmittance of the liquid crystal display device according to the second embodiment.

FIG. 9 is an equivalent circuit diagram for describing a liquid crystal display device according to a third embodiment.

FIG. 10 is a drive voltage waveform diagram for explaining a method of driving the liquid crystal display device according to the third embodiment.

FIG. 11 is a diagram showing a relationship between a liquid crystal applied voltage Vlc and transmittance in the liquid crystal display device of Embodiment 3.

FIG. 12 is a diagram showing a change in transmittance of the liquid crystal display device according to the third embodiment.

FIG. 13 is an equivalent circuit diagram for explaining a conventional liquid crystal display device.

FIG. 14 is a driving voltage waveform diagram for explaining a driving method of a conventional liquid crystal display device.

FIG. 15 shows a liquid crystal applied voltage V in a conventional liquid crystal display device.
It is a figure which shows the relationship between 1c and transmittance | permeability.

FIG. 16 is a diagram showing a change in transmittance in a conventional liquid crystal display device.

[Explanation of symbols]

 1, 21, 31, 41 Gate electrode 2, 22, 32, 42 Source electrode 3, 23, 33, 43 Switching element 4, 24, 34, 44 Pixel electrode 5, 25, 35, 45 Common electrode 6, 26, 36 , 46 Liquid crystal capacitance 7, 27 Auxiliary electrode 8, 28, 38 Auxiliary capacitance

Continued on the front page F-term (reference) 2H093 NA16 NA65 NC21 ND06 ND39 ND54 ND60 5C006 AA01 AA14 AA16 AA17 AC27 AC28 AF44 AF51 BB16 BC03 BC12 FA14 FA22 FA24 FA47 FA51 FA56 5C080 AA10 BB05 CC03 DD05 DD06 DD08 EE03 EJ19 JJ19 EJ19 JJ19 EJ19

Claims (12)

[Claims] A switching element and a pixel electrode connected to the switching element are provided in a matrix, and an auxiliary electrode is provided between the pixel electrode and a common electrode disposed on the pixel electrode via a liquid crystal layer. A liquid crystal display device comprising: an auxiliary electrode forming a capacitor; a video signal application period in which a voltage corresponding to a video signal is applied between the pixel electrode and the common electrode; An auxiliary signal application period in which a voltage corresponding to an auxiliary signal is applied to the common electrode, and at least one of a common voltage applied to the common electrode and an auxiliary voltage applied to the auxiliary electrode, A liquid crystal display device which is different between the video signal application period and the auxiliary signal application period. 2. A switching element and a pixel electrode connected to the switching element are provided in a matrix, and a common electrode is arranged on the pixel electrode via a liquid crystal layer;
What is claimed is: 1. A liquid crystal display device comprising a storage capacitor formed between said pixel electrode and a gate electrode of said switching element, wherein a video corresponding to a video signal is applied between said pixel electrode and said common electrode. A signal application period, and an auxiliary signal application period during which a voltage corresponding to an auxiliary signal is applied between the pixel electrode and the common electrode, wherein a common voltage applied to the common electrode and an auxiliary signal applied to the gate electrode are applied. A liquid crystal display device wherein at least one of the gate electrodes is different between the video signal application period and the auxiliary signal application period. 3. A switching element and a pixel electrode connected to the switching element are provided in a matrix, and an auxiliary electrode is provided between the pixel electrode and a common electrode disposed on the pixel electrode via a liquid crystal layer. A method for driving a liquid crystal display device having an auxiliary electrode forming a capacitor, comprising: a video signal application period for applying a voltage corresponding to a video signal between the pixel electrode and the common electrode; An auxiliary signal application period for applying a voltage corresponding to an auxiliary signal between the electrode and the common electrode; and applying the video signal application period and the auxiliary signal application to at least one of the common electrode and the auxiliary electrode. A method for driving a liquid crystal display device in which different voltages are applied in different periods. 4. A switching element and a pixel electrode connected to the switching element are provided in a matrix, and a common electrode is arranged on the pixel electrode via a liquid crystal layer.
A method for driving a liquid crystal display device in which an auxiliary capacitor is formed between the pixel electrode and a gate electrode of the switching element, wherein a voltage corresponding to a video signal is applied between the pixel electrode and the common electrode. A video signal application period to be applied, and an auxiliary signal application period for applying a voltage corresponding to an auxiliary signal between the pixel electrode and the common electrode, and at least one of the common electrode and the gate electrode, A method for driving a liquid crystal display device, wherein different voltages are applied during the video signal application period and the auxiliary signal application period. 5. The method according to claim 1, wherein at least one of the common electrode and the auxiliary electrode is connected to the auxiliary signal during the auxiliary signal application period.
4. The method according to claim 3, wherein a voltage that changes to the above state is applied. 6. The method according to claim 1, wherein at least one of the common electrode and the gate electrode is provided during the auxiliary signal application period.
The method according to claim 4, wherein a voltage that changes to two or more states is applied. 7. An auxiliary signal application period is provided before and after a writing period for writing a voltage corresponding to a video signal to the pixel electrode via the switching element, and a voltage between the pixel electrode and the common electrode is provided. 7. The liquid crystal according to claim 3, wherein the liquid crystal is shifted to a polarity opposite to the video signal application period between an auxiliary signal application period before the writing period and an auxiliary signal application period after the writing period. 8. A method for driving a display device. 8. The method of driving a liquid crystal display device according to claim 3, wherein the auxiliary signal application period is set simultaneously for all pixels. 9. The driving method of a liquid crystal display device according to claim 3, wherein the auxiliary signal application period is set according to a timing at which a voltage corresponding to a video signal is written to each pixel electrode. . 10. The method according to claim 3, wherein a voltage exceeding a voltage range applied during the video signal application period is applied between the pixel electrode and the common electrode during the auxiliary signal application period. Or a driving method of the liquid crystal display device. 11. A one-field period is constituted by at least two or more sub-field periods including the video signal application period and the auxiliary signal application period, and each sub-field period corresponds to a video signal of a predetermined color component. The method according to claim 3, wherein a voltage is applied between the pixel electrode and the common electrode during the video signal application period. 12. The one field period includes a subfield period for displaying a red component, a subfield period for displaying a green component, and a subfield period for displaying a blue component. Or claim 1
2. The method for driving a liquid crystal display device according to any one of 1) to 1).